Electron Releases

Removes unreferenced C++ code found via codebase sweep (+7 / −222 across 21 files).

⚠️ Review ask: Several of these may indicate missing functionality rather than truly-unused code. I've flagged the ones that look suspicious below — please confirm whether these were intentionally left unwired or if there's a latent bug.

Possibly a bug, not just dead code

• ElectronNavigationUIData (deleted class) — Added in #17440 for extensions support but never instantiated. ElectronBrowserClient doesn't override GetNavigationUIData() to return it; code uses upstream ExtensionNavigationUIData directly. If this was meant to carry Electron-specific navigation data for extensions, it never did. cc @samuelmaddock

• InspectableWebContents::synced_setting_names_ — Added in #33120 "fix: settings not persisting across devtools loads" but the member is never populated or read. If DevTools synced-settings registration was meant to use this, it's not wired up. cc @codebytere

• friend class NativeWindowsViews in frameless_view.h — typo for NativeWindowViews (no extra 's'), added in #29600. Code compiles because the friendship was never exercised, but if NativeWindowViews was meant to access private members here, it currently can't. cc @mlaurencin

• BuildMenuItemWithImage(..., GtkWidget*) header signature — the implementation actually takes const gfx::Image&. The header declared a function that never existed. Corrected the signature to match the impl.

Straightforward dead code

• CertificateManagerModel: removed ImportUserCert, ImportCACerts, ImportServerCert, Delete, and is_user_db_available_ — forked from Chrome's cert manager UI, but only the PKCS12 import path is used by app.importCertificate()
• gtk_util::GetOpenLabel / GetSaveLabel — orphaned by #42045 when Linux file dialogs moved to //ui/shell_dialogs (cc @codebytere)
• WinFrameView::GetReadableFeatureColor — implementation removed in #48568, header declaration left behind (cc @codebytere)
• AutofillDriverFactory::AddDriverForFrame + CreationCallback — DriverForFrame() creates on demand, explicit-add path never invoked
• ZoomLevelDelegate::SetDefaultZoomLevelPref — only the getter is used
• AutofillPopup::selected_index_ — declared, never read or written
• Forward decls: WebDialogHelper (class removed in #30663), ChromeContentRendererClient, ElectronNativeWindowObserver, ValueStoreFactory (redundant with existing include)

Not in this PR

ProxyingWebSocket::additional_headers_ is also dead (iterated but never populated) — same bug exists in upstream Chromium. Handling separately.

Notes: none